1. Field of the Invention
This invention relates to shears, and more particularly to a new and improved removable cutting tool insert assembly for shears fed with stock, such as bar stock.
2. Prior Art
Shears are heavy duty machines designed for continuous production of metal blanks such as flats, bars and billets used for such operations as forging and extruding. Automotive valves, nuts and bolts, wrenches, piston pins, gears etc. are just a few of the high volume parts formed from sheared blanks. Of the many types of cutoff machines available to volume users of billets and bars (round, square or other), flats, angles, channels and other standard mill shapes, few can match the speed and efficiency of the shear.
Two types of cutting tools used in shears are die and knife respectively, and the shear normally is equipped with top and bottom cutting tool housings, which usually are part of the main frame of the shear, with the bottom cutting tool housing being stationary and the top cutting tool housing being movable in a vertical direction and driven either mechanically as by a crankshaft and flywheel type drive, or fluidly, as by a hydraulic motor. In addition, one of the most important considerations in precision shearing is that the workpiece or stock be held as rigidly as possible. The main or parent part of the stock being fed in must be rigidly held as close to the shear area as practically possible to prevent any upward movement (i.e. ("kicking"). Similarly, the length or blank being sheared must be securely supported to prevent downward movement (i.e. "bending"), during the shearing stroke. These hold down and work-support units also generally are part of the main frame of the shear, and usually each works independently.
Considering shears employing knife type cutting tools or the like, U.S. Pat. No. 2,148,248 is pertinent in that it discloses a spring biased hold down on each side of the cutting knives or punches, as well as a resilient work support for one of two strips. However, this cutting tool is not an insert assembly and rather than a single shear, the cutting action is like a punch press operation wherein two parts are cut off, with one receding with the punch and die and the other remaining stationary. Likewise, U.S. Pat. No. 3,451,298 is pertinent because it discloses a positive hold down and a movable work support, both in a tool insert assembly for a shear. However, this is a rather complicated device, the hold-down is not resiliently biased, and the work-support is only partial and moves laterally instead of being biased for vertical movement.
The following U.S. patents are of interest, but less pertinent. U.S. Pat. No. 377,780 discloses an eccentric shear which is provided with a resiliently biased hold down, but does not disclose a work support beyond the shearing zone. U.S. Pat. No. 1,712,723 merely discloses a pitman shear with a hold down, but no work support. U.S. Pat. No. 1,854,516 discloses a combined angle bar shearing and hole punching mechanism but lacks a spring biased hold down and work support. An arm-like member only holds down the bottom flange of an already severed angle bar prior to punching.
As for shears employing die type cutting tools or the like, each of the following six U.S. patents is pertinent from the standpoint of a positive grip cut off feature, most disclosing a fixed die which acts as a hold down, and a movable cut off die. However, usually neither one is resiliently mounted, and these patented mechanisms are quite complex in comparison to the invention. The only patent which clearly discloses a tooling insert assembly is U.S. Pat. No. 3,972,257. The movable die is resiliently mounted, and therefore provides a resilient work support; however, the fixed die is not so resiliently mounted.
The remaining patents in this group are of less pertinence. U.S. Pat. No. 3,204,504 discloses a rather complicated device actuated by a punch, and neither the fixed die nor movable cut off die halves are resiliently mounted. While the latter are resiliently biased apart, this bias is overcome upon actuation of the device. U.S. Pat. No. 3,621,745 merely discloses a clamping or hold down fixed die and a work support or movable die. U.S. Pat. No. 3,735,656 differs in that it is directred to a complex impact die shear with rigid hold down and resilient cut off dies, stock bending being prevented by reverse axial pressure applying members. U.S. Pat. No. 4,086,832 discloses a holding die for necking down a bar and a cut off blade for shearing the necked down part. However, there appears to be neither a work support beneath the cut off blade nor a resilient mounting of the holding die. Finally, U.S. Pat. No. 4,152,959 discloses hydraulic die shearing of hot billets employing a fixed ring die and a movable ring die, neither one of which appears to be resiliently mounted.
In any event, none of the aforesaid patents, in either group, discloses, in a cutting tool insert assmbly for stock fed shears, the combination of movably mounted hold down and work support means for effectively preventing upward movement (i.e. "kicking") of the parent stock and downward movement (i.e. "bending") of the blank respectively, during shearing, resulting in close cut to length blanks and square cuts without distortion or burred edges, as perhaps found in other types of cut off operations.